Apparatus And Method For Solvent Recovery From Drying Process

ABSTRACT

Method and apparatus for condensing a majority of the solvent in a process gas stream at low temperatures, e.g., below the freezing point of water, ca. −5° C. The gas stream exiting the condenser step may be further processed in one or more emission control devices, such as a single or multi-step series of concentrator devices, such as zeolite concentrator devices. One or more emission control operations can be carried out downstream of the single or multi-step concentrators. The aforementioned condensing process enables the one or more concentrators to operate in a favorable temperature range for removal of 99% or more of VOC, thereby meeting or exceeding strict environmental regulations.

BACKGROUND

In the manufacture of lithium ion batteries and the like, a wet coatingmay be applied to a substrate in a slurry or paste form and is composedof fine powders mixed with a binder material, typically a polymer whichmay be water-soluble. In some cases, the binder is dissolved in aninorganic solvent such as N-methyl-2-pyrrolidone (NMP), acetone, variousalcohols or similar industrial solvent selected to dissolve the organicbinder to form a coatable liquid. These web-based products may be coatedon at least one face (side) of the substrate web. In these cases, a wetcoating is applied continuously or discontinuously on a moving web anddried in an oven or dryer to remove solvent thereby solidifying theapplied coating. Throughout this application a continuously appliedcoating shall be understood as applying a coat to a substrate, like aweb, foil, or the like in continuous process with or without timelyand/or locally varying coating parameters (e.g. thickness, chemicalcomposition and/or physical parameters of the coating material, etc.),whereby this continuous process shall also include the coating inregular or irregular patterns on a substrate continuously moved throughthe coating process.

In certain cases, the aforementioned web-based products are coated onboth faces (side) of the substrate web. In typical cases wherein bothfaces of the substrate web are to be coated, a first web coating isapplied continuously on a moving web and dried in an oven or dryerfollowed by application of a second wet coating which is subsequentlydried in a second drying step.

In a preferred embodiment for production of battery electrodes, the wetslurry is applied to both sides of the foil web and subsequently driedin an oven or dryer. This arrangement is referred to as simultaneousdual-side coating and drying. In the case of lithium ion electrodemanufacture, this arrangement is particularly advantageous in enhancingproductivity, needing only one drying step following application of thewet coating slurry to both side.

Recovery of VOC solvent emissions from these and other industrialprocess, such as solvents condensable at operating temperatures oftypical chilling systems (e.g., N-methyl-2-pyrrolidone (NMP) andtriethyl phosphate, dimethylacetamide (DMAc)), or other condensablefluids from an industrial operation such as the manufacture of lithiumion battery electrode, or drying and curing of polymeric films typicallyinvolves condensing the volatile organic compounds (VOC) along withwater and other potential contaminants in low temperature coils havingfinned surfaces and additional mist removal devices. In the case of manyuseful solvents such as NMP, the concentration exiting the condenseroperation is well above accepted limits for discharge into theatmosphere. In addition, recovery of such solvents may be cost-effectiveand desirable. Hence additional downstream emission control operations(emission control devices) are generally necessary to reduce the VOCconcentration to permissible levels. VOC capture and or destructionmethods include thermal (catalytic and straight thermal) oxidizers,scrubbers, carbon adsorption and adsorption on concentrator medias sucha zeolite. Acceptable emission concentrations for VOC discharge toatmosphere are typically in the range of 10 to 20 mg/Nm³ as carbon.

Current market conditions for the production of green energy goods suchas electrodes for batteries demand a much lower concentration level ofVOC emissions, on the order of 1 to 2 mg/Nm³. Conventional emissioncontrol devices are impractical choices in reaching these low levels.Moreover, energy consumption is high for most of the conventionalemission control methods and some or all of these devices as currentlyconfigured in the marketplace are incapable of reaching such low outletemission concentrations. VOC capture operations with condensing coilsrequire extremely low temperatures to reach equilibrium vapor pressuresnecessary to emit sufficiently low VOC concentrations exiting thecondensing unit. For instance, with NMP in the incoming air stream, inorder to reach 1 mg/Nm³ in the effluent stream the condensing coilswould need to run with coil surface temperatures below −35° C. Mostdrying processes also include water vapor in the dryer exhaust alongwith the VOC species. Such temperature conditions often result infreezing of water on the coil fins and tubes building ice, whicheventually blocks the airflow passages between tubes and the fins in theheat exchange core of condensing coil thereby requiring a thawing tomelt and remove the ice blocking the coil. In order to operatecontinuously, some systems may be arranged with two or more condensingcoil sets in parallel. Additional valves, heaters and air movinghardware are provided such that one or more condensing coil path is online in condensing operation mode while at least one condensing coilpath is isolated from the effluent flow path and is operating in thawmode. Issues of reliability and energy efficiency often plague suchsystems to the point they are avoided altogether.

Accordingly, an apparatus and method of reducing or eliminating suchVOCs that does not suffer from the drawbacks of the prior art would behighly beneficial.

SUMMARY

Problems of the prior art have been addressed by embodiments disclosedherein, which provide a method and apparatus for overcoming thelimitations of the prior art in an innovative and useful way bycondensing a majority of the solvent in a process stream at lowtemperatures (e.g., even below the freezing point of water, ca. −5° C.)compared to conventional thermal coil condensers. The remaining solventin the gas stream may be below 50 mg/Nm³ owing to the low temperaturecondensing step. In this temperature range solvents such as NMP or DMAcexhibit anti-freeze behavior depressing the freezing point of thewater-solvent mix thus avoiding buildup of ice. In certain embodiments,the gas stream exiting the condenser step is further processed in one ormore emission control devices, such as a single or multi-step series ofconcentrator devices, such as zeolite concentrator devices. Theaforementioned condensing process enables the one or more concentratorsto operate in a favorable temperature range resulting in the removal of90 to 99% or more of VOCs, thereby meeting or exceeding strictenvironmental regulations.

Concentrator flow capacity per given volume of adsorbent media isgenerally higher at lower removal percentages and is reduced at higherremoval percentages. Therefore the optimal design point for percentageremoval of VOC's for a particular solvent laden air stream in each stagebeing handled with two or more emission control devices in series, thefirst being a concentrator type, may be in the lower portion of therange of 90 to 99% removal. In one example embodiment, a first stepconcentrator removes 90% of VOC, leaving less than 10% of the incomingamount, e.g., leaving 5 mg/Nm³ when the incoming amount is 50 mg/Nm³. Anoptional second step concentrator device also removes≥90% of theincoming VOC from said first step concentrator. The resulting exitconcentration is therefore on the order of about 0.5 mg/Nm³, meetingstrict environmental regulations, including the new goals of the batteryindustry, for example.

Accordingly, certain embodiments disclosed herein relate to acirculation air conditioner such as for a recirculating air dryer ordryers generating circulation air laden with at least one condensablefluid (such as NMP), the circulation air conditioner comprising:

at least one main condenser having a feed port and an exhaust port andat least one main condensation stage, comprising:

-   -   i. a condensation chamber being accessible by or permeable for        the circulation air, and    -   ii. a cooling coil at least partially arranged inside said        condensation chamber and permeated by a cooling medium,    -   iii. whereby the cooling coil of said main condenser is operated        with a main cooling medium temperature of 0° C. or less,    -   b. a circulation air feed line being connected to said feed port        of said main-condenser and being connectable to a source of        condensable fluid laden air such as an exhaust circulation air        duct of said dryer or dryers for carrying the circulation air,    -   c. a circulation air exhaust line being connected to said        exhaust port of said main condenser and being connectable to a        feed circulation air duct of said dryer or dryers, and    -   d. a side-stream off gas extraction line being fluidly connected        to at least said condensation chamber of said main condenser,        -   i. whereby a volume flow of a circulation air streaming in            said condensation chamber is split into a high volume            re-circulation stream leaving the condenser through the            circulation air exhaust line and a low volume off-gas side            stream.

In certain examples, the side-stream and the re-circulation stream aresplit in volume by a split-ratio between 0.1% and 20%, preferablybetween 0.5% and 10%, and even more preferably between 1% and 5%.

In certain aspects, the circulation air conditioner may further compriseat least a pre-condenser with at least one pre-condensation stage thatis placed in the circulation air stream upstream of the main condenserand comprises a pre-condenser condensation chamber being accessible byor permeable for the circulation air, and a cooling coil at leastpartially arranged inside said pre-condenser condensation chamber andpermeated by a pre-cooling medium, whereby the pre-cooling medium has atemperature higher than the main cooling medium temperature.

The pre-condenser and said main-condenser may be enclosed in a commoncondenser housing.

The circulation air conditioner of any of the foregoing embodiments,alone or in combination, may further comprise a pre-cooling heatexchanger arranged upstream of the pre-condensation stage or at leastupstream the main condensation stage to already reduce a temperature ofthe streaming in circulation air and/or a reheating heat exchanger beingarranged downstream of the main condensation stage. The pre-cooling heatexchanger and the re-heating heat exchanger may be thermally coupled bythe exchange of a heat transfer medium such as water, brine or suitablethermal fluid and/or thermally coupled by a thermocouple or heat pipe.In some examples, the pre-cooling heat exchanger and the re-heating heatexchanger are in addition or alternatively thermally coupled via atleast one thermocouple or heat pipe.

The circulation air conditioner of any of the foregoing embodiments,alone or in combination, may further comprise an air pollution controlunit fluidly connected to the side-stream off gas extraction line andhaving at least one adsorptive concentrator with a gas exhaust and adesorption exhaust as a first pollution control stage and at least asecond pollution control stage being selected from the group consistingof a filtration device, an absorptive concentrator, a thermal oxizider,and a catalytic device. The second pollution control stage may comprisean adsorptive concentrator that is feed by the gas exhaust of the firstpollution control stage and having a gas exhaust and a desorptionexhaust. The desorption exhaust of at least one of the adsorptiveconcentrators may be connected to a desorption line, which is connectedto a desorbate condenser, whereby a gas exhaust of the desorbatecondenser is fed back into the side-stream off gas extraction line. Thesecond pollution control stage may comprise at least one activatedcarbon filter.

In its method aspects, embodiments disclosed herein relate to a methodfor conditioning a circulation air laden with at least one condensablefluid, comprising:

-   -   a. providing the circulation air at a first volume flow and        intake temperature level well above 0° C. to a main condenser        with at least one main condensation chamber;    -   b. gradually cooling the circulation air to a main temperature        level of 0° C. or less inside the main condensation chamber;    -   c. splitting the volume flow of the circulation into a high        volume re-circulating flow and low volume off-gas side stream        after reaching the second temperature level; and    -   d. providing the high-volume re-circulating flow to a        circulation air intake of a dryer.        In certain aspects, the method may further comprise providing a        condenser to cool the circulation air according to step b),        which comprises at least one cooling coil filled with a cooling        medium, and whereby the cooling medium enters the coiling coil        at the far end side of an circulation air entry with entry        temperature of 0° C. or less and is heated while traveling        through the cooling coil in a counter-flow direction to the        circulating air. The flow and temperature of the entering        cooling medium are preferably measured with a suitable flow        meter device and temperature sensor such as a resistance        temperature detector (RTD) respectively. The circulating flow        may be driven by a fluid pump in communication with the fluid        entry connection of the cooling coil. Further, the temperature        of the air exiting the cooling coil is preferably measured with        an array of one or more temperature sensors spaced across the        cross-section of the exit face of the coil. Said air temperature        sensors may be, for example, RTD's or thermocouples. The        temperature of the entering cooling media may be controlled to a        pre-determined set point by a suitable PID controller in control        communication with a valve and actuator positioned in the        conduit from the chilled brine source, typically a water-cooled        or air-cooled centrifugal chiller. A three-way flow path valve        set allows fresh cooling media from the cooling media source to        enter the circulating flow path through the coil while heated        cooling media in fluid communication with the cooling media        return connection is discharged back to the cooling media        source. Alternatively, the temperature of the air exiting the        cooling coil may be controlled to a pre-determined set point by        a second suitable PID controller in control communication with a        valve and actuator positioned in the conduit from the chilled        brine source. In a most preferred embodiment the output from        said exit air temperature measurement and controller are        configured to calculate by control algorithm the temperature set        point for the entering cooling media control loop which is        transmitted in a cascade control arrangement between the two        respective PID controllers. In some embodiments, the controller        may have a processing unit and a storage element. The processing        unit may be a general purpose computing device such as a        microprocessor. Alternatively, it may be a specialized        processing device, such as a programmable logic controller        (PLC). The storage element may utilize any memory technology,        such as RAM, DRAM, ROM, Flash ROM, EEROM, NVRAM, magnetic media,        or any other medium suitable to hold computer readable data and        instructions. The controller unit may be in electrical        communication (e.g., wired, wirelessly) with one or more of the        operating units in the system, including one or more of the        valves, actuators, sensors, etc. The controller also may be        associated with a human machine interface or HMI that displays        or otherwise indicates to an operator one or more of the        parameters involved in operating the system and/or carrying out        the methods described herein. The storage element may contain        instructions, which when executed by the processing unit, enable        the system to perform the functions described herein. In some        embodiments, more than one controller can be used.

The method of any of the forgoing embodiments, alone or in combination,may still further comprise feeding the circulation air at the firstvolume flow to a pre-condenser upstream said main-condenser with apre-condensing temperature level below a first temperature level andwell above said main condensing temperature; gradually cooling thecirculation air to said pre-condensing temperature level in thepre-condenser; and providing the cooled circulation air to an intake ofsaid main condenser. The circulation air may be pre-cooled upstream ofsaid main condenser, and/or may be reheated downstream of said maincondenser.

The method of any of the forgoing embodiments, alone or in combination,may still further comprise feeding the off-gas side stream to an atleast two-stage air pollution control device; collecting and increasingthe concentration of residual condensable fluid in an adsorptiveconcentrator as a first pollution control stage; and subsequentlytreating the remaining off gas stream in a second air pollution controldevice as a second stage further downstream of the first stage to alevel of concentration of residual condensable in the air well below apredetermined limit, such as 1 mg/Nm³. The second air pollution controldevice may be a second adsorptive concentrator or a filtration device,such as an active carbon filter.

By operating a single or multi-stage condenser in combination with oneor more emission control devices, such as two VOC concentrator wheels inseries, the target emission of <1 mg/Nm3 is obtainable. In someembodiments, recovery of VOC solvents results in elimination of nearlyall VOC waste products to the environment without requiring thermalcombustion products or other secondary pollutants. Valuable solventssuch as NMP may be recovered and purified for reuse in the batteryelectrode manufacturing process in a closed-loop fashion, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments disclosed herein may take form in various components andarrangements of components, and in various process operations andarrangements of process operations. The drawings are only for purposesof illustrating preferred embodiments and are not to be construed aslimiting. This disclosure includes the following drawings:

FIG. 1 is a schematic diagram of an exemplary single-stage condenser anddownstream emission control apparatus in accordance with certainembodiments;

FIG. 1a is a schematic diagram of an exemplary single-stage condenserand downstream emission control apparatus in accordance with anembodiment including an air-to-air economizer;

FIG. 2 is a schematic diagram of an exemplary multi-stage condenser anddownstream emission control apparatus in accordance with certainembodiments;

FIG. 3 is a process diagram of a first exemplary process in accordancewith certain embodiments;

FIG. 4 is a process diagram of a second exemplary process in accordancewith certain embodiments;

FIG. 5 is a schematic diagram of a direct contact condenser operation inaccordance with certain embodiments; and

FIG. 6 is a schematic view of a multi-stage adsorption/desorption unit.

DETAILED DESCRIPTION

A more complete understanding of the components, processes andapparatuses disclosed herein can be obtained by reference to theaccompanying drawings. The figures are merely schematic representationsbased on convenience and the ease of demonstrating the presentdisclosure, and is, therefore, not intended to indicate relative sizeand dimensions of the devices or components thereof and/or to define orlimit the scope of the exemplary embodiments.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawing, and are not intended to define or limit the scope of thedisclosure. In the drawing and the following description below, it is tobe understood that like numeric designations refer to components of likefunction.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used in the specification, various devices and parts may be describedas “comprising” other components. The terms “comprise(s),” “include(s),”“having,” “has,” “can,” “contain(s),” and variants thereof, as usedherein, are intended to be open-ended transitional phrases, terms, orwords that do not preclude the possibility of additional components.

All ranges disclosed herein are inclusive of the recited endpoint andindependently combinable (for example, the range of “from 2 inches to 10inches” is inclusive of the endpoints, 2 inches and 10 inches, and allthe intermediate values).

As used herein, approximating language may be applied to modify anyquantitative representation that may vary without resulting in a changein the basic function to which it is related. Accordingly, a valuemodified by a term or terms, such as “about” and “substantially,” maynot be limited to the precise value specified, in some cases. Themodifier “about” should also be considered as disclosing the rangedefined by the absolute values of the two endpoints. For example, theexpression “from about 2 to about 4” also discloses the range “from 2 to4.”

It should be noted that many of the terms used herein are relativeterms. For example, the terms “upper” and “lower” are relative to eachother in location, i.e. an upper component is located at a higherelevation than a lower component, and should not be construed asrequiring a particular orientation or location of the structure. As afurther example, the terms “interior”, “exterior”, “inward”, and“outward” are relative to a center, and should not be construed asrequiring a particular orientation or location of the structure.

The terms “top” and “bottom” are relative to an absolute reference, i.e.the surface of the earth. Put another way, a top location is alwayslocated at a higher elevation than a bottom location, toward the surfaceof the earth.

The terms “horizontal” and “vertical” are used to indicate directionrelative to an absolute reference, i.e. ground level. However, theseterms should not be construed to require structures to be absolutelyparallel or absolutely perpendicular to each other.

Turning now to FIGS. 1 and 2, where like numerals indicate like parts,there is shown a condenser 10 having a feed port 12 and an exhaust port14 spaced from the feed port 12. In the embodiments shown, the entry ofcondenser 10 has optionally an air particulate removal filter 18, one ormore pre-cooling regions 15, each having a pre-cooling chamber 15 a; oneor more cooling or condensing regions or stages 16, downstream of theone or more pre-cooling regions 15, each having a condensing chamber 16a; a mist coalescing panel (i.e., a demister) 28, and one or morere-heating regions 17, downstream of the one or more cooling orcondensing regions 16, each having a re-heating chamber 17 a. Each ofthe aforementioned chambers is accessible by or permeable for thecirculation of air. In certain embodiments, the cooling or condensingregion 16 may be a single stage condenser (FIG. 1), or may comprisemultiple cooling stages (FIG. 2), each effective to further cool theentering gas stream to a temperature lower than the temperature to whichthe gas stream was cooled in the cooling stage immediately upstream ofit.

In some embodiments, there are two cooling or condensing regions 16, 16′(FIG. 2). In some embodiments, there are three, four, five or morecondensing regions (not shown). The number of condensing regions dependsin part on the properties of the VOC's and how gradual the VOC-ladenprocess stream should be cooled to avoid fog formation; i.e., it is atleast in part a function of the rate of temperature drop or temperaturecooling profile of the VOC's.

In certain embodiments, each cooling or condensing region or stage 16may include a condensation chamber 16 a having a cooling coil 20arranged therein, through which a cooling medium may be circulated.Suitable cooling media are not particularly limited, and include waterand brines, such as water mixed with propylene and/or ethylene glycol.Each cooling coil 20 may be partially or completely arranged within itsrespective cooling or condensing region 16. As shown in FIG. 1,preferably the flow of cooling media through the cooling coil 20 is in acounter-flow direction to the flow of process gas through thecondensation chamber 16 a.

Alternatively, a spray condenser could be used where the coolant issprayed in the condensation chamber by one or more nozzles to condensethe VOC's in the process stream.

Alternatively still, as shown in FIG. 5, a direct-contact condenser 510could be arranged in place of condenser 10 of FIGS. 1-4. Solvent-ladenairflow 70 from a drying operation is directed to direct-contactcondenser vessel 505 after precooling in economizer heat exchanger 101.The cooled stream 70 a is optionally pre-filtered in air filter unit 569and pressurized by blower 502 and blown into a port in the lower sectionof vessel 505. The solvent laden air 570 enters the lower chamber of 505and is directed vertically through flow distributor 516 into a region ofmedia packing 515. Flow distributor 516 includes structural elements tosupport the weight of the packing and weight of liquid adhering to thepacking. Said packing may be selected for optimum surface contact areawith the upward-flowing air stream per unit volume and for low pressuredrop characteristics. Common packing shapes include Raschig rings,saddles, pall rings or other suitable packing shapes. The packing isgenerally of corrosion resistant material such as stainless steel,ceramic or polymeric materials. The solvent-laden air stream 570 passesthrough the packing media and directly contacts cooled condensed solventflowing downward by gravity and wets the surfaces of the packing. Saidcooled condensed solvent is fed to the upper portion of vessel 505 viaflow distribution header 513 and may optionally be further distributedby fluid tray 514 to evenly distribute the cooled solvent evenly acrossthe horizontal cross section at the top of the packing 515. Cooledsolvent 538 is used directly as condensing media by direct contactbetween solvent laden air stream 570 and the wetted surfaces of thepacking media in the packing contact region 515. The cooled solventtrickles downward through the packing picking up condensed solvent fromthe counter flowing air eventually reaching the bottom of packing region515 and drains through distributor 516 into the lower section of vessel505 acting as a sump. The level of collected solvent 536 in said sump ismaintained by a level sensor and control which directs solvent throughconduit 537 to primary storage vessel 38.

The exit gas flow 571 passes through a demister element 528 and amajority of the flow travels through exhaust line 72 a and is reheatedin economizer 10 before being conveyed in conduit 72 to the dryeroperation. The split ratio of flow conducted in conduit 30 is preferablyin the range of 0.5% to 10% of the flow in exhaust line 572. Duringunsteady state operating conditions this split ratio can be as high as20%. The flow in conduit 30 is preferably reheated by heat exchanger 580to obtain a temperature of flow 30 b entering the concentrator 50between 10° C. and 20° C., most preferably 15° C.

It is to be appreciated that for direct contact condensation, thecooling and condensation surface is in effect the cooled solvent liquidacting as the cooling media as well wetting the surface of the packingand trickling downward countercurrent to the solvent-laden airflow.Having a lower vapor pressure than the solvent laden air, the cooledsolvent picks up more solvent from the air as well as increasing intemperature from said air. Therefore in continuous steady stateoperation energy must be removed from the condensed solvent stream 539by liquid-liquid heat exchanger 591. The temperature of the cooledsolvent fed into the direct condenser must be measured and preciselycontrolled prior to distributing the cooled solvent into vessel 505 viafeed manifold 513. A majority of the collected solvent in 536 in thesump region of 505 is directed through conduit 539 and optionallyfiltered in liquid filter 518 and further pumped by centrifugal pump 592and cooled through liquid-liquid heat exchanger 591 and further conveyedto distribution header 513 near the top the tower vessel 505. The splitratio of the flow in conduit 537 is in the range of 5% to 30% of theflow in conduit 539. The flow rate in 539 is measures with a suitableliquid flow meter and controlled to a set point by a controllermodulating the speed of motorized pump 592 by variable frequency motorspeed control. The temperature of the cooled solvent is measured as itenters the distributor manifold 513 by a suitable temperature elementsuch as an RTD and controlled to a set point temperature, preferably inthe range of −10 to 0° C., most preferably −4° C. by coolant brinesource 520 in exchanger 591. An actuated flow control valve in thecoolant flow conduit from brine source 520 is modulated to obtain adesired measured temperature feeding the distributor 513. Saidtemperature set point is sufficiently cool such that the vapor pressureof the solvent in the gas phase exiting the packing region 515 resultsin a concentration level of solvent in stream 571 in the range of 1 to500 mg/Nm3, preferably 1 mg/NMP in the case of NMP.

In certain embodiments, the pre-cooling region 15 and the re-heatingregion 17 may be brought and/or maintained at their respective operatingtemperatures with a pre-cooling heat exchanger and a re-heating heatexchanger. In certain embodiments, these heat exchangers are a closedloop heat exchange recirculation system 35 which may function as aneconomizer. The recirculation system 35 may include a first coil 35 a atleast partially arranged inside the pre-cooling chamber 15 a and asecond coil 35 b at least partially arranged inside the pre-heatingchamber 17 a. The loop 35 may contain a suitable heat exchange mediumsuch as water or brine to transfer heat to and/or from the process gasin the pre-cooling and pre-heating regions. An air-to-air economizerheat exchanger 101 also could be used as shown in FIG. 1 a. Exhaust flow70 from the drying operation is precooled in economizer 101 by thecooler temperature return air flow in exhaust line 72 a. The economizer101 is selected to provide thermal exchange effectiveness in the rangeof 40 to 60% resulting in temperature of flow 70 a at the properpre-cooled temperature value in the range of 80 to 100° C. Accordingly,the exhaust return air 72 a is reheated with energy from exhaust 70 to adesired temperature in the range of 40 to 60° C. in the economizer 101.The temperature of the heat exchange medium optionally may be regulatedwith the aid of a further heat exchanger 291 as shown in FIG. 3. Incertain embodiments, the temperature of the coolant in the recirculationloop 35 is higher than the temperature of the coolant in the coil orcoils in the condensation region 16. Excess thermal energy may beremoved to control the temperature of the coolant in recirculation loop35 by circulating a portion of the coolant from loop 35 via pump 292through a liquid-liquid heat exchanger 291, in a split ratio range of 10to 50% of the flow through 35. The portion of fluid thus cooled isreturned in conduit 293 to 35 before entering 35 b.

In certain embodiments, the pre-cooling region 15 and the condenserregion 16 have a common housing. In certain embodiments, the condenserregion 16 and the re-heating region 17 have a common housing. In certainembodiments, the pre-cooling region 15, the condenser region 16 and thepre-heating region 17 have a common housing.

In some embodiments, a pre-cooling heat exchanger 35 a may be arrangedupstream of the pre-cooling region to reduce the temperature of thestreaming in circulation air. In some embodiments, a re-heating heatexchanger 35 b may be arranged downstream of the condensation region 16.In some embodiments, both heat exchangers may be so arranged. Thepre-cooling heat exchanger and the re-heating heat exchanger may bethermally coupled by the exchange of a heat transfer medium such aswater, brine or suitable thermal fluid.

In certain embodiments, a side-stream off gas extraction line 30 may beprovided in fluid communication with the condensation region 16. Wheremultiple condensation regions 16 are provided, the side-stream off gasextraction line is preferably in direct fluid communication with thefurthest downstream condensation chamber 16 a; i.e., the chamberimmediately upstream of the re-heating region 17. The side-stream gasextraction line 30 may be configured to communicate with a downstreamunit operation, such as one or more VOC concentrators and/or one or moreemission control units as discussed in greater detail below. A portionof side-stream off-gas may also be extracted following the re-heatingregion through conduit 29 and added to the side-stream flowing inextraction line 30. Temperature control loop 31 comprised of atemperature sensor and controller positioned to measure the mixtemperature of flows from extraction lines 29 and 30 and modulateactuated flow dampers in flow lines 29 and 30. Thus an optimumtemperature in the range of 10 to 18° C., preferably 15° C. may beobtained and controlled by closed-loop control of flow proportioning asthe flow 30 b enters the concentrator 50. A circulation air exhaust line72 may be provided in fluid communication with the exhaust port 14 ofthe condenser 10. The circulation air exhaust line 72 may be configuredto connect to a feed circulation air duct of one or more industrialdryers (FIG. 3), for example. The split flow proportion flowing inconduit 30 a is preferably in the range of 0.5% to 10% of the flow inexhaust line 72. During unsteady state operating conditions this splitratio can be as high as 20%.

In some embodiments, the feed port 12 of the condenser 10 is in fluidcommunication with, or is adapted or configured to be in fluidcommunication with, the exhaust from one or more industrial dryers 100(FIG. 3), such as by a circulation air feed line 70. That is, the sourceof the process gas to the condenser 10 may be the exhaust from one ormore industrial dryers, such as one or more dryers drying coating on aweb. For example, in battery electrode manufacturing, a wet process isused to apply battery electrode components to a current collector web ofcopper or aluminum foil, for example. Typically a polymer binder,graphite, and an active material are mixed with a solvent, or water, andapplied to a web. The solvent or water is driven off in one or moredryers to produce a dry battery electrode material for use in a batterycell. The exhaust from such a dryer or dryers is a suitable feed streamto the condenser 10.

In some embodiments, the exhaust port 14 of the condenser 10 is in fluidcommunication, or is adapted or configured to be in fluid communication,with a recirculation feed to one or more industrial dryers 100 (FIG. 3),such as by a circulation air exhaust line 72. A suitable driving force,such as a suction fan arranged in the recirculation line 72, may be usedto drive the flow of process gas into and through the condenser 10.

The dryer or dryers 100 may be a conventional convection air web dryersuch as where hot air is used to dry a coating on a web travellingthrough the dryer. For example, air bars or nozzles may be used todirect a jet of air to impinge on the surface of a material to carry outheat and/or mass transfer functions. Convection air drying of batteryelectrode materials is typically carried out with drying airtemperatures in the range of 80 to 160° C. and air nozzle convectionheat transfer coefficients to the web from 30 to 100 watts/m²° C. perside of web. As is known to those skilled in the art, a plurality of airnozzles may be arranged in an array or multiple arrays to direct airimpingement over a large surface of a material in web form, either onone side of the web, or both sides simultaneously. In some embodiments,the heat transfer to the web may be enhanced by addition of infraredemitters or emitting surfaces. Optimum temperatures for said emittingsurfaces are in the range of 260 to 425° C. Web materials commonlyprocessed in this manner include paper, plastic film, metal foils, wovenand non-woven fabrics and mats, and porous membrane materials. Flotationair bars are a type of air nozzle used in industrial dryers and ovens tofloatingly support and convey a continuous web to be processed bythermal treatment, which may include any combination of drying, heating,curing or cooling of the web. A coating is applied to the surface of theweb or a volatile material is present within the base web material whichmust be dried and/or heated to a particular temperature so as tofacilitate thermal curing of a polymer material in the coating. In manyprocesses the volatilized materials within the web or coating afterbeing liberated from the web surface are carried away from that surfaceby the spent nozzle air and conducted by an air handling system to anexhaust. This exhaust is then directed into the condenser 10 inaccordance with certain embodiments.

Alternatively, the dryer may be a so-called “inert” dryer, in which thedryer interior contains an inerting gas such as nitrogen in order tolimit the oxygen content (e.g., to 2% or less) of the dryer atmosphereto, for example, reduce the possibility of explosion. Said nitrogen maybe vaporized from liquid nitrogen storage tanks or produced continuouslyfrom nitrogen generator systems having membrane separators or pressureswing adsorption modules.

Recovered condensate may be removed from the condenser 10 and stored ina suitable container 38. Each condensing stage 16 and 16 a′ andcoalescing demister 28 are configured to drain condensed solvent bygravity to sump basin 36. Drain line 37 includes an air lock (s-trap orother suitable device) to prevent passage of air from condenser 10 tocontainer 38 and vice versa.

In certain embodiments, the pre-heating stage(s) 15 of the condenser 10functions as a pre-condenser; it is operated at a suitable temperature(and/or pressure) such that little or no VOC's condense as the processgas flows through the one or more pre-heating chambers 15 a.

Most preferably the cooling coil 20 in the condenser stage 16 isoperated so that the gas exiting condenser chamber 16 a has a maintemperature of 0° C. or less. In some embodiments, where multiplecondenser stages 16 are used, the cooling coil arranged in the stagefurthest downstream is operated such that the chamber in which it isarranged has an exit temperature of 0° C. or less, such as at 0° C., −1°C., −2° C., −3° C., −4° C., −5° C., or down to −20° C. in cases wherethe anti-freeze behavior due to solvent in the solvent-water mix isfavorable against freezing and ice formation in the condensing coil. Forsuch low temperature condensing it is especially important the coolingcoil(s) be arranged in the one or more upstream condenser stages andoperated such that their respective chambers have higher temperaturessuch that only a small portion of the VOC's in the upstream stages arecondensed.

It is a goal of each condenser coil design and operating condition tomaximize condensation with wetting of solvent on the tube and finnedsurfaces to promote capture and gravity drainage. Rapid cooling of thesolvent laden air below equilibrium vapor pressure of the solventpromotes the formation of tiny droplets within the bulk air stream as ittravels between condensing coil tube and finned surface. Afternucleation, said tiny droplets tend to remain very small with negligiblefurther condensation and growth owing to the Kelvin effect. Accordingly,in order to reduce or eliminate deleterious fogging, in certainembodiments the rate of cooling is carefully controlled so as not tocool the VOC-laden stream too rapidly. Fogging, or the formation of verysmall droplets (generally on the order of 1 micron or less) of liquid,is problematic in that it involves the formation of tiny droplets thattend to become entrained in the air flow, thus hindering their removalor recovery. Indeed a significant fraction of such aerosol droplets passthrough demister panels as well as pass through the core of thecondenser coil. As a result, fog or aerosol formation results in theundesirable loss of product. In embodiments where the VOC includes NMPsuch as in lithium battery electrode production, for example, these tinydroplets of NMP end up being returned to the dryer(s), which is highlyundesirable. Accordingly, the pre-cooling region(s) 15 and thecondensation region(s) 16 should be operated such that gradual coolingof the process stream takes place so as to avoid fog formation.

For purposes of cooling rate characterization and quantification, theresidence time of the solvent laden air while within the core of aparticular condensing coil (i.e. while undergoing cooling) is made on asuperficial volume basis. That is, the volume space occupied by thetubes and fins within the overall dimensions of the core is ignored incalculating the superficial residence time. The specific volumetricairflow Q through the coil is expressed in normal cubic meters per unittime. The coil face area and depth in the flow direction are used tocalculate the volume V in cubic meters. Therefore the superficialresidence time in the core is determined as t=V/Q. Further, thetemperature drop DT in Centigrade degrees (note this parameter is atemperature difference value, not an absolute temperature value) of theair and solvent driven by the cooling coil may be measured directly inoperation or calculated from supplier sizing data in the design phase.Finally the rate of cooling R may be expressed as R=DT/t. For example, acooling coil core has a face area of 4.5 square meters and a flow pathdepth of 0.3 meters. The specific volumetric airflow is 25,000 Nm³/h.Therefore the residence time may be calculated as t=(4.5×0.3)m³/25,000m³/hr=5.4×10⁻⁵³ hr. Converting to milliseconds t=5.4×10⁻⁵ hr×3,600,000millisec/hr=194 milliseconds. If the air temperature entering the coilis 56° C. and the exiting temperature is 28° C. the cooling rateR=DT/t=(56° C.−28° C.)/194=0.144 C degrees per millisecond.

For NMP capture with minimal fog formation in the condensing coilregions where condensation of solvent is occurring while the gas flowtravels the distance between the condensing coil tubes and finnedsurfaces, the rate of cooling should be less than 0.30 C degrees permillisecond, preferably between 0.15 and 0.22 C degrees per millisecond.Typical design criteria for organic solvents such as DMAc with watervapor for minimal fog formation in the condensing coil regions wherecondensation of solvent is occurring while the gas flow travels thedistance between the condensing coil tubes and finned surfaces the rateof cooling should be less than 0.3 C degrees per millisecond, preferablybetween 0.12 and 0.2 C degrees per millisecond. In most cases theacceptable maximum cooling rates for a particular solvent must bedetermined by experiment.

In operation the method of precise control of the cooling rate may beillustrated in reference to FIG. 2 for exemplary case of coil 16 a. Thissame method is applicable to a plurality of cooling coils represented as16′ within a condensing plenum 10. It is to be understood that thecirculating flow loop and controls described below shall apply toadditional coils in like manner. All such flow loops shall include andthe temperature control circuits and hardware shown for coil 16 a.

The flow and temperature of the cooling medium 20 a entering the coil 16a are preferably measured with a suitable flow meter device andtemperature sensor such as a resistance temperature detector (RTD)respectively. The circulating flow is driven by a fluid pump 21 a incommunication with the fluid entry connection of the cooling coil 16 a.Further, the temperature of the air entering the cooling coil ispreferably measured with an array of one or more temperature sensors 21d spaced across the cross-section of the entry face of the coil and thetemperature of the air exiting the cooling coil is preferably measuredwith an array of one or more temperature sensors 21 c spaced across thecross-section of the exit face of the coil. Said air temperature sensorsmay be RTD's or thermocouples. The temperature of the entering coolingmedia is measured and controlled to a pre-determined set point by asuitable sensor and PID controller 21 b in control communication with avalve and actuator 21 positioned in the conduit 20 c from the chilledbrine source, typically a water-cooled or air-cooled centrifugalchiller. An actuated three-way flow path valve 21 allows fresh coolingmedia from the cooling media source 20 c to enter the circulating flowpath through the coil while heated cooling media in fluid communicationwith the cooling media return connection 20 b is discharged back to thecooling media source. Alternatively, the temperature of the air exitingthe cooling coil is controlled to a pre-determined set point by a secondsuitable PID controller 21 c in control communication with a valve andactuator 21 positioned in the conduit from the chilled brine source. Ina most preferred embodiment, the output from said exit air temperaturemeasurement and controller 21 c is configured to calculate by controlalgorithm and transmit in a cascade control arrangement said temperatureset point to the entering cooling media control loop 21 b.

In certain embodiments, once the process gas flow from the condenserregion 16 has reached 0° C. or less and VOC condensation is complete orsubstantially complete, the gas flow is divided into a relatively highvolume recirculation gas flow (e.g., line 72) and a relatively lowvolume off-gas side stream (e.g., extraction line 30). In the exampleshown in FIG. 3, those volumes are split by a split-ratio ofapproximately 2%.

In certain embodiments, the blend of off-gas side stream extractionlines 29 and 30 combining into 30 a is adapted or configured to beplaced in fluid communication with one or more downstream emissioncontrol operations 40. For example, the emission control operation mayinclude at least one adsorptive concentrator with a gas exhaust and adesorption exhaust, such as one or more VOC adsorptive concentrators 50used to concentrate the VOC's extracted by the condenser 10. The type ofVOC concentrator(s) used is not particularly limited, and may berotation type gas adsorption concentration devices. For example,honeycomb rotors may be used to support the VOC adsorbent media, and therotor may be divided into at least an adsorption zone and a desorptionzone. The solvent-laden air to be processed is passed through theadsorption zone, where the VOC's are adsorbed by the adsorbent media(e.g., zeolite). The VOC's can then be desorbed, such as by passingheated air through the desorption zone. In some cases, suchconcentrators may include a rotor wheel having an adsorbent substratesuch as a hydrophobic zeolite, or a combination of adsorbents. The rotorwheel may be rotated continuously, and the airstream passes through therotor wheel concentrator where VOC's are stripped from the air andadsorbed onto the adsorbent substrate. The majority of this now cleanair may then be exhausted to atmosphere. A small portion of the airstream may be heated to an elevated temperature to be used as desorptionair. Continuous rotation of the wheel transports this air stream to thedesorption region, where the VOC's are heated, desorbed and collected.Purge air may be used to cool the adsorbent media, and the now heatedpurge air can be recycled to the desorption region. Thus, the one ormore adsorptive concentrator 50 may have a gas exhaust and a desorptionexhaust and function as an emission or pollution control stage.

In certain embodiments, a single VOC concentrator 50 may be used. Inother embodiments, two or more VOC concentrators 50 may be used,arranged in series. In some embodiments, one or more further emission orpollution control stages 52 may be used downstream of the one or moreVOC concentrators 50, such as one or more filtration devices (e.g.,activated carbon based filtration devices), absorptive concentrators,thermal oxidizers (e.g., regenerative thermal oxidizers), catalyticoxidizers and/or biofilters.

In some embodiments, a two-stage air pollution control unit 500 as shownin FIG. 6 may be arranged downstream of the condenser 10, such as thepollution control unit disclosed in JP 2011-031159. The unit includes anorganic solvent recovering device wherein an adsorbing body comprisingan adsorbing element containing an adsorbent is constituted of at leastan adsorbing region, a regeneration region and a cooling region. Theorganic solvent-containing gas (e.g., the gas in the side-stream 30 fromthe concentrator 10) is continuously supplied to the adsorbing region ofthe adsorbing body, the adsorbing element adsorbing the organic solventin the adsorbing region, and is sent to the regeneration region todesorb the adsorbed organic solvent from the adsorbing element by aheated gas. The organic solvent-containing gas is again adsorbed in theadsorbing region by the regenerated adsorbing element, and a condensingpart for recovering the organic solvent desorbed in the regenerationregion is provided. A backup treatment device capable of performingcontinuous adsorbing and desorbing treatment of the organicsolvent-containing treated gas passed through the adsorbing regionwithout being adsorbed is provided, and is constituted so that thecontinuous solvent adsorbing and desorbing treatment is performed in theadsorbing region and the regeneration region by the adsorbing elementformed into a columnar or cylindrical shape.

FIGS. 3 and 4 illustrate exemplary embodiments of the operation of acondenser and emission control apparatus. In an exemplary embodiment asshown in FIG. 3, an exhaust gas stream 70 containing VOC's, such as NMP,that is exiting one or more dryers 200 may have a temperature generallybetween about 80-130° C., more typically between about 120-130° C., andmay have a solvent concentration generally between about 500-3000 ppmV,more typically between about 1800-2500 ppmV. In the embodiment shown,the concentration of solvent in the exhaust stream is 1800 ppmV and thetemperature is 130° C. A driving force such as a fan 201 may be used tocause the exhaust stream to enter the feed port 12 of a condenser 10.Alternatively or in addition, a suction fan 202 may be placed downstreamof the condenser exhaust port 14.

Consistent with the objective of gradually reducing the temperature ofthe exhaust gas stream, it first enters a pre-cooling region 15 of thecondenser 10, the region 15 having a coil 35 a with a cooling mediumhaving a temperature sufficient to lower the temperature of the gasstream to about 83° C. The residence time of the gas stream in thepre-cooling region should be sufficient to allow the temperature of thestream to cool to the desired value, such as 83° C. Since nocondensation is occurring in this stage, cooling rates in the range of0.6 C degree per millisecond or more are acceptable. Preferably theconditions in the pre-cooling region 15 are such that little or nosolvent condensation occurs. The gas then flows into a first cooling orcondensing stage 16, where it is cooled by a coil 116 a containing acooling medium having a temperature sufficient (e. g., 18° C.) to lowerthe temperature of the gas steam to 29° C. In this stage most of theheat exchange is sensible heat and although little condensation ofsolvent occurs in this stage the cooling rate is critical in this earlystage of condensing solvent. Cooling rates not to exceed the range of0.15 to 0.30 C degree per millisecond are preferred. The cooled gas thenflows into a second cooling or condensing stage 16′, or main condensingstage, equipped with a coil 116 b containing a cooling medium having atemperature sufficient (e.g., −10° C.) to lower the temperature of thegas stream to equal to or less than 0° C.; e.g., −2° C., wheresignificant phase change occurs, and all or substantially all of theremaining solvent condenses. Again, in this stage the cooling rate iscritical as in this early stage of condensing solvent. Cooling rates notto exceed the range of 0.15 to 0.30 C degree per millisecond arepreferred. This gradual cooling of the gas stream helps minimize orprevent deleterious fog formation. In addition, causing the coolingfluid in the coils 116 a, 116 b to flow from the downstream side to theupstream side (i.e., in the direction opposite to the direction depictedin FIG. 3) can reduce fog formation.

A major portion of the gas then flows into the re-heating region 17,which in the embodiment shown has a coil 35 b containing a coolingmedium having a temperature sufficient to raise the temperature of thegas stream to 45° C., after which it is recirculated to the one or moredryers 200 via exhaust line 72. Ambient air may be added to the exhaustline 72 as shown at 73.

A minor portion (e.g., by mass flow balance equivalent to the flow ofgas entering into web slots in the one or more dryers) of the gas flowis extracted from the cooling or condensing stage 16′ via a side-streamoff gas extraction line 30. In the example shown in FIG. 4, the volumesof the re-circulation air stream and the off gas side-stream are splitby a split-ratio of approximately 1.1%. It is preferred that thisextraction be carried out upstream of the pre-heating region 17, sincethe relatively low temperature of this extracted stream raises theefficiency of a downstream concentrator. A portion of the gas in there-heating region 17 may be extracted in conduit 29 and mixed with thegas in the side-stream off gas extraction line 30 extracted from thesecond cooling or condensing region 16′. The amount of gas that has beenre-heated in region 17 that is mixed with the gas in the side-stream offgas extraction line can be blended with temperature controller anddamper system 31 to regulate the temperature of the gas entering adownstream concentrator (or other downstream emission control apparatus)to optimize the performance of the downstream unit, such as regulatingthe gas in the side-stream off gas extraction line 30 to a temperatureof about 10-20° C., preferably about 16-18° C. NMP can be recovered fromthe condenser 10 via line 117 and stored as shown.

Thus, the condenser apparatus 10 can be used to produce a feed stream toa downstream emission control unit or units, such as one or more VOCconcentrators, the feed stream being at an optimum temperature for theperformance of the emission control unit or units. Off-gas side streamflows extracted from a plurality of condenser apparatuses equivalent tocondenser apparatus 10 may be preferably combined in common duct 700 andfed to a single VOC polishing concentrator system as shown in in FIGS. 3and 4. This allows for better capacity matching of the side stream flowsfrom a large operation having for instance 8 or more condensingapparatuses. Combination of the off-gas side stream flows results inimproved economy of scale for the VOC polishing operation.

The gas in the side-stream off gas extraction line enters a first VOCpolishing concentrator 50 which contains an adsorbent such as a zeoliteor carbon. This first concentrator 50 typically removes from about90-99% of the VOC's (e.g., NMP) from the gas stream. The adsorbed VOCsmay be then desorbed by reheating, and may be directed to a cooling ordesorbant condenser 80 or the like and recirculated back to the inletstream to the first VOC polishing concentrator as shown. VOC condensatemay be collected from the condenser 80 via line 81 and stored orrecycled to the coating process.

In the embodiment shown, the concentrated gas stream next enters asecond VOC polishing concentrator 50′, which also typically removes fromabout 90-99% of the VOC's (e.g., NMP) remaining in the stream. Incertain embodiments, the second VOC polishing concentrator 50′ isidentical to the first VOC polishing concentrator 50. The collected airstream may be condensed in the condenser 80 as shown.

A bypass line 85 may be provided to allow interruption of theconcentrator units, the bypass line 85 directing the flow (e.g., withthe aid of fan 88) to one or more back-up carbon filters 87, forexample, so that the content of the VOC's exhausted to atmosphere doesnot exceed regulatory limits (e.g., <1 mg/Nm³).

An emergency purge system 90 is provided, which includes purge line 91having a damper 92 that directs the flow of gas from the condenser 10 toone or more emission control units, such as one or more carbon filters95.

FIG. 4, where like numerals indicate like parts to those describedabove, illustrates a similar process with only a single VOC polishingconcentrator 50 being employed. In this embodiment, two carbon filters87, 87′ are arranged downstream of the single VOC polishing concentrator50 in order to achieve the target VOC emission concentration of <1mg/Nm³. This embodiment also eliminates the emergency purge system 90,instead a purge fan 190 is fluidly connected to the exhaust line 72 asshown to provide an emergency purge.

As in the case of coil condensers 10, avoidance of fog formation indirect contact condensers 510 depends on gradual cooling of thesolvent-laden air stream in the condensing region, that is within theheight of packing 515. Cooling rate is first considered in the designselection of the volume of packing section 515. Condenser vessel 505 ispreferably circular in cross-section. Alternatively it may be of squareor rectangular cross-section in plan view in order to accommodate sitelayout requirements. Similar to the case of coil type condensers, thevolume is determined on a superficial volume basis. That is, the volumespace occupied by the packing within the overall dimensions of thepacking region 515 is ignored in calculating the superficial residencetime. The specific volumetric airflow Q through the coil is expressed innormal cubic meters per unit time. The packing face area and depth inthe flow direction are used to calculate the volume V in cubic meters.Therefore the superficial residence time in the core is determined ast=V/Q. Further, the temperature drop DT in Centigrade degrees (note thisparameter is a temperature difference value, not an absolute temperaturevalue) of the air and solvent driven by the cooling coil may be measureddirectly in operation or calculated from supplier sizing data in thedesign phase. Finally the rate of cooling R may be expressed as R=DT/t.For example, a direct-contact condenser vessel has a face area of 4.0square meters and a packing height of 1.5 meters. The specificvolumetric airflow is 25,000 Nm³/h. Therefore the residence time may becalculated as t=(4.0×1.5)m³/25,000 m³/hr=2.4×10⁻⁴ hr. Converting tomilliseconds t=2.4×10⁻⁴ hr×3,600,000 millisec/hr=864 milliseconds. Ifthe air temperature entering the packing is 83° C. and the exitingtemperature is −4° C. the cooling rate R=DT/t=(83° C.−(−4)° C.)/864=0.1C degrees per millisecond.

For NMP capture with minimal fog formation in the condensing packingregions where condensation of solvent is occurring while the gas flowtravels the distance within the packing, the rate of cooling should beless than 0.20 C degrees per millisecond, preferably between 0.07 and0.15 C degrees per millisecond. Typical design criteria for organicsolvents such as DMAc with water vapor for minimal fog formation in thecondensing coil regions where condensation of solvent is occurring whilethe gas flow travels the distance within the packing the rate of coolingshould be less than 0.15 C degrees per millisecond, preferably between0.05 and 0.12 C degrees per millisecond. In most cases the acceptablemaximum cooling rates for a particular solvent must be determined byexperiment.

In operation the method of precise control of the cooling rate may beillustrated in reference to FIG. 5 for exemplary case of packing 515.The flow meter 524 and temperature sensor 521 monitor flow rate andtemperature of the cooled solvent medium entering the manifold 513. Thecirculating flow 539 is driven by a fluid pump 592 in communication withthe fluid entry connection of the cooling coil 591. Further, thetemperature of the air entering the packing 515 is preferably measuredwith an array of one or more temperature sensors 522 spaced across thecross-section of the entry face of packing, and the temperature of theair exiting the demister 528 is preferably measured with an array of oneor more temperature sensors 523 spaced across the cross-section of theexit face of the demister. Said air temperature sensors may be RTD's orthermocouples. The temperature of the entering cooled solvent media ismeasured and controlled to a pre-determined set point by a suitablesensor and PID controller 521 in control communication with a valve andactuator positioned in the conduit 520 from the chilled brine source,typically a water-cooled or air-cooled centrifugal chiller. The measuredair temperature drop of the air 522 entering the packing and the air 571exiting the condensing tower is controlled to a pre-determined set pointby a second suitable PID controller 523 in control communication withthe variable frequency motor control driving pump 592. In this mannerthe target rate of temperature drop in the condensing unit 510 iscontrolled to 0.15 C degrees per millisecond for NMP for example.

FIG. 6 illustrates a different type of adsorption device to replace thesingle VOC polishing concentrator in FIG. 4. The main adsorption takesplace on the path A1 through the first segment of a carousel-typeadsorption concentrator 610. The desorption is done with reference toJP2011031159A. A main desorption cycle is performed by the path B2 witha condenser 620 and a heating coil 625 implemented. Additional the FIG.6 shows a closed-loop auxiliary adsorption-cooling-desorption circlewith the path ‘“A2” (adsorption)—“C” (cooling)—heating—“B1”(desorbing)—cooling’. This configuration has the advantage that the twocircles can be operated under inert conditions (if necessary) and canlead higher desorption concentrations in the main desorption circle. Asdescribed in FIG. 4 additional carbon filter can be implemented beforethe gas is released to the stack. The descripted process is alsopossible with a disc-type concentrator.

While various aspects and embodiments have been disclosed herein, otheraspects, embodiments, modifications and alterations will be apparent tothose skilled in the art upon reading and understanding the precedingdetailed description. The various aspects and embodiments disclosedherein are for purposes of illustration and are not intended to belimiting. It is intended that the present disclosure be construed asincluding all such aspects, embodiments, modifications and alterationsinsofar as they come within the scope of the appended claims or theequivalents thereof.

What is claimed is:
 1. Circulation air conditioner for a recirculatingair dryer generating circulation air laden with at least one condensablefluid, comprising: a. at least one main-condenser having a feed port andan exhaust port and at least one main condensation stage, comprising:ii. a condensation chamber being accessible by or permeable for thecirculation air, and iii. a cooling coil at least partially arrangedinside said condensation chamber and permeated by a cooling medium, iv.whereby the cooling coil of said main condenser is operated with a maincooling medium temperature of 0° C. or less, b. a circulation air feedline being connected to said feed port of said main-condenser and beingconnectable to a source of condensable fluid laden air for carrying thecirculation air, a. a circulation air exhaust line being connected tosaid exhaust port of said main-condenser, and b. a side-stream off gasextraction line being fluidly connected to at least said condensationchamber of said main condenser, i. whereby a volume flow of acirculation air streaming in said condensation chamber is split into ahigh volume re-circulation stream leaving the condenser through thecirculation air exhaust line and a low volume off-gas side stream. 2.The circulation air conditioner of claim 1, further comprising at leasta pre-condenser with at least one pre-condensation stage a. being placedin the circulation air stream upstream the main-condenser b. andcomprising i. a pre-condenser condensation chamber being accessible byor permeable for the circulation air, and ii. a cooling coil at leastpartially arranged inside said pre-condenser condensation chamber andpermeated by a pre-cooling medium, iii. whereby the pre-cooling mediumhas a temperature higher than the main cooling medium temperature. 3.The circulation air conditioner of claim 2, whereby said pre-condenserand said main-condenser are enclosed in a common condenser housing. 4.The circulation air conditioner according to claim 1, further comprisinga pre-cooling heat exchanger being arranged upstream saidpre-condensation stage to already reduce a temperature of the streamingin circulation air and/or a reheating heat exchanger being arrangeddownstream of the main condensation stage.
 5. The circulation airconditioner of claim 4, wherein the pre-cooling heat exchanger and there-heating heat exchanger are thermally coupled by the exchange of aheat transfer medium such as water, brine or suitable thermal fluidand/or thermally coupled by a thermocouple or heat pipe.
 6. Thecirculation air conditioner according to claim 1, further comprising anair pollution control unit being fluidly connected to said side-streamoff gas extraction line and having at least one adsorptive concentratorwith a gas exhaust and a desorption exhaust as a first pollution controlstage and at least a second pollution control stage being selected fromthe group consisting of a filtration device, an absorptive concentrator,a thermal oxizider, and a catalytic device.
 7. The circulation airconditioner according to claim 6, wherein the second pollution controlstage comprises of an adsorptive concentrator being fed by said gasexhaust of the first pollution control stage and having a gas exhaustand a desorption exhaust.
 8. The circulation air conditioner of claim 6wherein the desorption exhaust of at least one of the adsorptiveconcentrators is connected to a desorption line, which is connected to adesorbate condenser, whereby a gas exhaust of said desorbate condenseris feed back into the side-stream off gas extraction line.
 9. Thecirculation air conditioner of claim 7 wherein the desorption exhaust ofat least one of the adsorptive concentrators is connected to adesorption line, which is connected to a desorbate condenser, whereby agas exhaust of said desorbate condenser is feed back into theside-stream off gas extraction line.
 10. The circulation air conditionerof claim 6 wherein the second pollution control stage comprises of atleast one activated carbon filter.
 11. A method for conditioning acirculation air laden with at least one condensable fluid, comprising:a. providing the circulation air at a first volume flow and intaketemperature level well above 0° C. to a main condenser with at least onemain condensation chamber; b. gradually cooling the circulation air to amain temperature level of 0° C. or less inside the main condensationchamber; c. splitting the volume flow of the circulation into a highvolume re-circulating flow and low volume off-gas side stream afterreaching the second temperature level; and d. providing the high-volumere-circulating flow to a circulation air intake of a dryer.
 12. Themethod according to claim 11, further comprising providing a condenserto cool the circulation air according to step b), which comprises atleast one cooling coil filled with a cooling medium, and whereby thecooling medium enters the coiling coil at the far end side of ancirculation air entry with entry temperature of 0° C. or less and isheated while traveling through the cooling coil in a counter-flowdirection to the circulating air.
 13. The method according to claim 11,further comprising: a. feeding the circulation air at the first volumeflow to a pre-condenser upstream said main-condenser with apre-condensing temperature level below a first temperature level andwell above said main condensing temperature; b. gradually cooling thecirculation air to said pre-condensing temperature level in thepre-condenser; and c. providing the cooled circulation air to an intakeof said main condenser.
 14. The method according to claim 12, furthercomprising: a. feeding the circulation air at the first volume flow to apre-condenser upstream said main-condenser with a pre-condensingtemperature level below a first temperature level and well above saidmain condensing temperature; b. gradually cooling the circulation air tosaid pre-condensing temperature level in the pre-condenser; and c.providing the cooled circulation air to an intake of said maincondenser.
 15. The method according to claim 11, further comprisingpre-cooling said circulation air upstream of said main condenser. 16.The method according to claim 11, further comprising re-heating saidcirculation air downstream of said main condenser.
 17. The methodaccording to claim 15, further comprising re-heating said circulationair downstream of said main condenser.
 18. The method according to claim11, further comprising: a. feeding the off-gas side stream to an atleast two-stage air pollution control device; b. collecting andincreasing the concentration of residual condensable fluid in anadsorptive concentrator as a first pollution control stage; c.subsequently treating the remaining off gas stream in a second airpollution control device as a second stage further downstream of thefirst stage to a level of concentration of residual condensable in theair well below a predetermined limit.
 19. The method of claim 18,wherein said predetermined limit is 1 mg/Nm³.
 20. The method accordingto claim 18, wherein said second air pollution control device is asecond adsorptive concentrator.
 21. The method according to claim 18,wherein said second air pollution control device is a filtration device.22. The method according to claim 21, wherein said filtration devicecomprises an active carbon filter.